The present invention relates generally to the field of watercraft, and more particularly to the field of marine propulsion systems, and specifically to a transmission having two forward speeds and reverse for an inboard/outboard stern drive watercraft.
In conventional single speed marine drives, an engine is mechanically coupled to a propeller either directly or through a gearbox to provide a single gearing ratio. It is known that a single gear ratio connection between the engine and propeller will provide less than optimal performance for many applications. There have been efforts to improve the performance of marine propulsion systems by the use of multi-speed and hydraulically coupled transmissions. It is known that the performance of a watercraft may be improved by providing a higher gear ratio connection between the engine and the propeller for low speed operation and acceleration, and by providing a direct drive or overdrive gear ratio between the engine and the propeller for high speed operation. In this manner, the engine may be operated at a point closer to its peak power output during a wider range of operating conditions.
U.S. Pat. No. 5,711,742 issued on Jan. 27, 1998, to Leinonen, et. al., incorporated by reference herein, describes a multi-speed marine propulsion system with an automatic shifting mechanism. An automatic transmission is interposed between the engine and the inboard/outboard drive apparatus. Although providing improved performance when compared to prior art single speed propulsion systems, the device of Leinonen creates an excessively long driveline that necessitates the placement of the engine in a more forward position within the watercraft hull than may otherwise be desirable.
U.S. Pat. No. 4,820,209 issued on Apr. 11, 1989, to Newman, incorporated by reference herein, describes a marine propulsion system having a fluid coupling with a variable power output. While this system avoids the long driveline of the Leinonen apparatus, it does so at the expense of multi-speed forward gear ratios. In lieu of multi-speed gears, the device of Newman provides for a controlled slippage between the engine and the propeller in order to improve low speed watercraft operation. The hydraulic coupling and forward-reverse gearing of the Newman transmission are enclosed within a housing passing through the transom of the watercraft, which in turn connects to the vertical drive unit containing the propeller. The device of Newman fails to provide a direct mechanical connection between the engine and the propeller at a plurality of forward gear ratios.
Thus, there is a particular need for an improved multi-speed mechanical drive transmission for a stern drive watercraft. Accordingly, a transmission for a watercraft is described herein as including: a generally horizontal input shaft rotatably supported by the vertical drive unit housing and adapted for coupling to an engine output shaft of the watercraft; a generally vertical output shaft rotatably supported by the vertical drive unit housing and adapted for coupling to a propeller gear apparatus; a bevel gear apparatus selectively connectable between the input shaft and the output shaft in one of a high forward, reverse and neutral positions for providing a high forward ratio of rotation between the input shaft and the output shaft, a reverse ratio of rotation between the input shaft and the output shaft, and neutral connection between the input shaft and the output shaft respectively; a planetary gear apparatus having a sun gear connected for rotation with a portion of the bevel gear apparatus, a planet gear having an axis of rotation connected for rotation with the output shaft, and a ring gear; a brake selectively connected between the vertical drive unit housing and the ring gear, the brake having an engaged position for providing a low forward ratio of rotation between the input shaft and the output shaft and a disengaged position for allowing independent rotation of the sun gear and the planet gear.
In another embodiment, a transmission for a stern drive watercraft is described herein, the stern drive having a vertical drive unit housing disposed rearward of a transom of the watercraft, the transmission including: a generally horizontal input shaft rotatably supported by the vertical drive unit housing and adapted for coupling to an engine output shaft of the watercraft; a generally vertical output shaft rotatably supported by the vertical drive unit housing and adapted for coupling to a propeller gear apparatus; and a bevel gear apparatus selectively connectable between the input shaft and the output shaft for alternatively providing a first forward gear ratio connection, a second forward gear ratio connection, a reverse gear ratio connection, and a neutral connection between the input shaft and the output shaft.